About Sofia-SIP

Sofia-SIP is an open-source SIP
User-Agent library, compliant with the IETF
RFC3261 specification (see the
feature table).
It can be used as a building block for SIP client software for uses such as VoIP, IM, and
many other real-time and person-to-person communication
services. The primary target platform for Sofia-SIP is
GNU/Linux. Sofia-SIP is based
on a SIP stack developed at the Nokia
Research Center.
Sofia-SIP is licensed under the LGPL.

Features

SIP features

Sofia-SIP implementation follows
RFC3261
and related key RFCs. INFO, UPDATE and REFER methods are supported.
Also supported is SIMPLE
presence and instant messaging, with the MESSAGE, SUBSCRIBE/NOTIFY and PUBLISH
methods. Features such as early sessions, provisional responses, early media,
caller preferences and session timers are included. Full set of transports,
including both TCP and UDP over either IPv4 or IPv6, is supported. Signaling
can be secured with SSL/TLS.
See the full SIP and SDP feature table.

SIP Offer-Answer module

Sofia-SIP provides an implementation of the SDP offer-answer negotiation as
specified in RFC3264. This
is an essential component in using SIP to establish media sessions such
as VoIP and video conferencing.

NAT traversal support

Support for STUN as
specified in RFC3489. STUN
functionality is available via a separate module, so it can also be
used independently from the base SIP stack. SIP extensions such as
symmetric response routing (RFC3581/rport) are supported as well.

Open development model

Sofia-SIP is run as a community effort: the development source tree is hosted
on a public server, the development discussions happen on public forums, and
there is a public development roadmap. Additionally, the project welcomes
new contributors and the project copyright is shared (i.e. no dual licensing).